1. Field of the Invention
The present invention relates generally to packaging for integrated circuits, and, more specifically, to high-performance packaging for monolithic microwave integrated circuits (MMICs) operable at frequencies in the 20 GHz range.
2. Description of the Related Art
Packaging techniques known to the prior art have been well documented. Known manufacturing techniques include cofired ceramic enclosures using thick-film metallization, glass-sealed ceramic enclosures using thin-film metallization, metal enclosures having ceramic feedthroughs, and metal enclosures having glass feedthroughs.
Since ceramic-package manufacture is a batch process, it has a distinct advantage over some of the other technologies available. If the yield of the process is high, ceramic packages should be low cost in reasonable volume.
Of the few cofired ceramic packages generally available for MMICs and power FETs, the main contributor to poor microwave performance is the lead feedthrough. In typical state-of-the-art designs, discontinuities exist due to the lead attachment, to passage of the conductor into and out from the ceramic wall, to changes in the conductor width, and to coupling of RF signals to the lid and lid sealing ring. These discontinuities introduce higher-order modes and reflections as a result of impedance mismatch, and contribute to overall poor feedthrough performance, especially at frequencies above 20 GHz.
An MMIC package capable of good performance in the 20 GHz range should have low insertion loss and voltage standing wave ratio (VSWR) per lead feedthrough, good isolation between leads, microstrip compatibility, and an electrical design approach extendable to higher frequencies. The present invention fulfills all of these goals in a package that is cascadable, bondable, and capable of extensive application throughout the entire MMIC industry, including military applications.